The present invention relates to a device for implantation in a human eye, having an electrode array or a microcontact structure for contacting nerve tissue in the visual system of the human eye. The present invention relates in particular to a visual prosthesis having a device for generating stimulation impulses, which are used to stimulate living tissue or nerves.
One frequent cause of the partial or full loss of eyesight is destruction of the photoreceptor layer in the retina of the human eye, after which incident photons are not converted into a corresponding stimulation of the ganglion cells. The ganglion cells are only partly affected by this pathology, so that an external stimulation of the ganglion cells still existing in the retina can generate a visual perception. On the basis of this, developments which involve the implantation of a microcontact structure for contacting intact ganglion cells have been carried out for some time.
Devices have already been developed in the form of implants for the retina of the human eye, which are intended for the treatment of patients who have partially or fully lost their eyesight owing to defects in the retina. A microelectronic device is in this case implanted in the region of the retina with a multiplicity of photosensitive pixel elements, via which an image projected onto the retina through the still intact lens of the eye is captured. In other visual prostheses, the image capturing is carried out using an external camera, in particular a video camera. The image captured by the pixel elements or the camera is converted into electrical signals and delivered via stimulation electrodes by means of electrical stimulation impulses to the ganglion cells of the retina or to the optic nerve, so as to restore or improve the eyesight of the blind or partially blind patient.
For epiretinal transmission of the stimulation impulses to the cells of the retina or to the cells of the optic nerves, microcontact structures are used which essentially consist of a support material that carries electrically conductive contact elements designed in the form of pins or needles on one side, which protrude from the plane of the support sheet and are distributed uniformly with a constant area density over the surface of the implant. The known visual prostheses, however, have the disadvantage that they entail a large space requirement. Owing to the particular sensitivity of the human eye and the extremely limited space inside the eye, it is in principle desirable to accommodate stimulation systems or the implants of the visual prostheses in as small a space as possible.
Another problem with known visual prostheses consists in supplying energy to the implants and their microcontact structure, or the surface of the electrodes. According to the present state of knowledge, an average power of about 40 mW is necessary for the energy supply of a retinal implant. Such a energy supply cannot be provided over a prolonged period of time by means of an implanted battery, since this would entail too great a space requirement.
Active retinal implants therefore require a energy supply unit which is independent of the system for generating the visual impression, lies outside the eye and operates without a wire connection to the retinal implant. DE 19705988 C2 discloses a subretinal implant, the implant being provided with a photovoltaic layer which is effective for light outside the visible spectrum. The energy supply is in this case carried out using infrared light. The retinal implant is provided with a surface tightly attached to the retina, the surface being provided with electrodes for stimulating cells of the retina. The current supply of the components of the implants inside the eye using infrared light may, however, entail the risk of thermal damage to the eye due to local heating inside the eye.